The importance of end-capping or terminating carbonate polymers with certain end or terminal groups is well known. Carbonate polymers which are not end-capped are generally insufficiently thermally stable since the free end phenolic hydroxyl groups provide reactive sites which are generally detrimental to the thermal stability of the polymers. Known and commonly used end-capping agents include the phenol compounds such as phenol itself, chroman-I, and paratertiarybutyl phenol.
Other end-capping agents are also known and used in the preparation of carbonate polymers. These include, inter alia, the alkanol amines disclosed in U.S. Pat. No. 3,085,992; the imides disclosed in U.S. Pat. No. 3,399,172; aniline and methyl aniline disclosed in U.S. Pat. No. 3,275,601; and the primary and secondary amines disclosed in U.S. Pat. No. 4,001,184. Some other end capping agents include the aromatic amines disclosed in U.S. Pat. No. 3,028,365; and the ammounium compounds, primary cycloalkyl amines and primary aliphatic or aralkyl amines disclosed in U.S. Pat. No. 4,111,910.
However, according to Schnell, Chemistry and Physics of Polycarbonates (1964), page 183, ammonium hydroxide and amines saponify polycarbonates back to the monomers. This is supported by Bolgiano in U.S. Pat. No. 3,223,678 wherein it is disclosed that small amounts of amines such as monoethanolamine and morpholine break or degrade polycarbonate into lower molecular weight polycarbonates. Thus, this area of chemistry is generally not completely understood and is one where the empirical approach is still generally the method used to determine whether a particular compound or class of compounds will function as effective end-capping agents for carbonate polymers. This area is further complicated by the fact that even though a particular compound may be an effective end-capping agent for carbonate polymers, its presence in the carbonate polymer may adversely affect the advantageous physical and mechanical properties of the carbonate polymer.